This invention relates to and has among its objects the provision of a novel method for detecting aflatoxin contamination in almonds.
Aflatoxins, a group of highly toxic substances produced by certain species of Aspergillus, especially A. flavus, have been found to occur in agricultural products such as corn, cottonseed, a variety of oilseeds, and many varieties of nuts. Experimental studies indicate that aflatoxins are acutely toxic to most animal species. The extreme toxicity of aflatoxin is demonstrated by the fact that the LD.sub.50 of the B.sub.1 component is less than 30 micrograms for day-old ducklings. Animals which consume sublethal quantities of aflatoxin for several days or weeks develop a subacute toxicity syndrome which commonly includes moderate to severe liver damage. Prolonged administration of the toxin at subacute levels leads to formation of cancerous liver tumors. Data accumulated from feeding tests indicate that the effective dose of the B.sub.I component of aflatoxin for the induction of liver tumors in rats is approximately 10 mg per day. When this value is compared with similar estimates for other hepatocarcinogens such as dimethylnitrosamine (750 mg/day) and butteryellow (9,000 mg/day), the relative potency of aflatoxin is readily apparent.
Aflatoxins occur at varying concentrations throughout the tissue of contaminated products and can occur at concentrations up to over 1,000,000 parts per billion (ppb) in individual nuts such as peanut kernels. These toxins may remain after the molds that produced them are removed or destroyed. Aflatoxins are fairly resistant to heat and to chemical treatments that do not destroy the nutmeat. conventional food processing, such as roasting nuts, can reduce the aflatoxin level but not sufficiently to solve the problem.
Aflatoxin contamination has been found in tree nuts such as walnuts and almonds. Infection of tree nuts with aflatoxigenic molds probably occurs most often in the field before and/or during harvest while the kernels are still moist. Intact shells appear to protect nuts from mold but damage to the shell by mechanical harvesting or insect infestation allow the mold to proliferate on the kernels while the nuts are still moist. In particulate foods, such as nuts, the toxins are confined to a relatively few units, and the solution to the aflatoxin problem is the removal of the contaminated units. In a survey of the almond crop in California, it was estimated that before processing about one kernel in 26,500 in-shell almonds is contaminated with aflatoxin; however, these kernels have, on the average, very high levels of aflatoxin, and thus it is essential that all contaminated nuts are removed.
Presently shelled almonds are sorted by a combination of electronic color sorting and manual sorting by trained personnel. Because aflatoxin content in almonds appears to be correlated with the number of seriously damaged kernels, removal of these kernels by commercial sorting procedures appreciably reduces aflatoxin contamination. However, because of the acute toxicity, mutagenicity, and carcinogenicity of aflatoxin, it is important that the removal of this toxin be maximized. Additionally, it is a common practice to use less seriously damaged kernels, i.e., almonds which are chipped or broken or have other minor damage affecting their appearance, to manufacture sliced and diced nuts, and this practice tends to increase the chance of aflatoxin contamination of such products due to the unavoidable inclusion of some seriously damaged nuts with the less damaged nuts normally used as manufacturing stock; even the standards for the best quality grades of shelled almonds include some tolerance for the inadvertent inclusion of seriously damaged kernels. Although there has been a long felt need, heretofore no ready method for detection of aflatoxin contamination in almonds has been known.
Studies on cottonseed and corn have shown that seed contaminated with A. flavus are often associated with a bright greenish-yellow (BGY) fluorescence. Investigators have reported that A. flavus isolated from BGY fluorescent cotton fibers produced kojic acid, which was converted to the BGY fluorescing substance by plant tissue peroxidase. In a study of pistachio nuts, kernels from nuts showing BGY fluorescence contained 50% of the aflatoxin in the samples studied. However, because A. flavus grew from only 21% of the kernels from fluorescent shells and 4% of the BGY fluorescent shells, the researchers concluded that fungi other than A. flavus produced BGY fluorescence in pistachio shells, but that BGY fluorescence may indicate that conditions have been favorable for growth of toxicogenic molds on pistachio nuts. Though the preceding was known, this information did not disclose or suggest any method for detecting aflatoxin contamination in almonds.